In a large bowl, combine the flour, granulated sugar, baking soda and salt.
In another bowl, beat the egg, vanilla and water and pour into the dry ingredients; whisk until combined. The batter should be thick enough to coat a spoon; add more water if its too thick.
In a wok, heat about 1-1/2 inches of oil (about 4 cups) to 350 degrees . Line a plate with paper towels.
Peel the bananas; slice them in half crosswise, then cut each piece in half lengthwise. When the oil is hot, dip the banana slices in the batter and slip them into the hot oil, frying 5 or 6 at a time. Fry, turning occasionally, until the fritters are golden, 2 to 3 minutes.
Drain the fritters on paper towellined plates and repeat with the remaining bananas. Sprinkle with the confectioners sugar and serve.